Log-frequency isocontours within and around myelo- and cytoarchitectonically defined auditory core (thick black lines), reconstructed from electrophysiological recording data reported in A of . (See Materials and Methods for details on contour rendering.) Thin dotted lines show shape of underlying coronal sections of exposed temporal plane and superior temporal gyrus; thick dashed line is estimate of A1/R border. A from was chosen for having the most extensive set of recording data over A1 and R, and for being representative of other datasets in and in other combined physiology/cytoarchitectonic experiments. Tonotopic progressions in macaque can generally be described as follows: wrapping around the caudal cap of the core is a corona of high BF neurons, with highest BF neurons near or slightly outside the core proper. This high-BF region tends to extend more than halfway along the medial edge of the core (moving rostrally), with BFs then dropping to mid or low frequencies. Continuing along the medial edge toward the rostral-most tip of the core, there is often a moderate increase from low to medium BFs. Progressing posteromedially to anterolaterally across the core, there is a steep drop from higher to lower BFs ending in a low BF rostrolateral trough. Along the lateral edge of the core, moving posterior to anterior, there is a steeper descent in BF that joins the low-BF trough. Finally, in some cases there is an increase from low-to-medium/high BFs moving out from the anterolateral edge of the less densely myelinated aspect of the core (for an almost complete low-to-mid BF gradient in R, see , their B).